1. Field of the Invention
The present invention relates to an organic electro-luminescence display device and a method for fabricating the same.
2. Discussion of the Related Art
Various kinds of flat panel display devices that can replace heavy and bulky cathode ray tubes (CRTs) have been recently developed. Examples of the flat panel display devices are liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panel (PDP) devices, and electro-luminescence display devices.
Many attempts have been actively made to improve the display quality of the flat panel displays and provide large-sized displays. Among them, the electro-luminescence display devices are self-luminous and display video images by exciting a phosphor material using carriers, such as electrons and holes. The electro-luminescence display devices are classified into inorganic electro-luminescence display devices and organic electro-luminescence display devices. While the inorganic electro-luminescence display devices require a high voltage of 100-200V, the organic electro-luminescence display devices can be driven at a low DC voltage of 2-20V. In addition, the organic electro-luminescence display devices have such advantages as wide viewing angle, rapid response time and high contrast ratio. Therefore, the organic electro-luminescence display devices can be used as a graphic display, a television monitor, or a surface light source. Further, because the organic electro-luminescence display devices are slim, lightweight and elegant in color vision, they are suitable for a next-generation flat panel display device.
A passive matrix type driving method is widely used for driving the organic electro-luminescence display devices, which does not require thin film transistors (TFTs). The passive matrix type driving method, however, has many limitations in resolution, power consumption, lifetime, and so on. Therefore, an active matrix type driving method has been researched and developed for a next-generation display device that requires a high resolution and large-size screen.
Hereinafter, an organic electro-luminescence display device according to the related art will be described with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view of an active matrix type organic electro-luminescence display device according to the related art. For convenience's sake, one pixel region including a red (R) sub-pixel, a green (G) sub-pixel, and a blue (B) sub-pixel is illustrated in FIG. 1.
Referring to FIG. 1, first and second substrates 10 and 30 are arranged to face each other. A TFT T is formed on a transparent substrate 1 of the first substrate 10 in each sub-pixel. An organic electro-luminescent layer 14 is formed on the TFT T and the first electrode 12. The organic electro-luminescent layer 14 contains light emission materials to display red, green and blue colors. A second electrode 16 is formed on the organic electro-luminescent layer 14. The first and second electrodes 12 and 16 apply an electric field to the organic electro-luminescent layer 14. The first substrate 10 on which the organic electro-luminescent layer 14 is formed is attached to the second substrate 30.
The active matrix type organic electro-luminescence display device illustrated in FIG. 1 has a bottom emission type structure. When the first electrode 12 and the second electrode 16 are respectively used as an anode and a cathode, the first electrode 12 is formed of a transparent conductive material and the second electrode 16 is formed of a metal having a low work function. Under this condition, the organic electro-luminescent layer 14 includes a hole injection layer 14a, a hole transporting layer 14b, an emission layer 14c and an electron transporting layer 14d, which are sequentially formed on the first electrode 12. The light-emitting materials for red, green and blue colors are arranged in the emission layers 14c of the sub-pixels.
In the organic electro-luminescence display device, the array element, including the TFT and the electrodes, and the organic electro-luminescent diode are stacked on the same substrate. The organic electro-luminescence display device is fabricated by attaching the substrate, on which the array element and the organic electro-luminescent diode are formed, to a separate substrate provided for encapsulation. In this case, the yield of the organic electro-luminescence display device is determined by the product of the yields of the array element and the organic electro-luminescent diode. Therefore, the entire process yield is greatly restricted by the process of forming the organic electro-luminescent diode. For example, even if the array element is successfully formed, the organic electro-luminescence display device becomes defective, when the organic electro-luminescent layer, which is generally a thin film having a thickness of about 1000 Å, has a defect cased by a foreign particle or other factors.
In addition, the bottom emission type organic electro-luminescence display device according to the related art has limitation in aperture ratio, although it has a high stability and high degree of freedom due to the encapsulation. Thus, it is difficult for the bottom emission type organic electro-luminescence device to be used for a high-definition product.
As for the top emission type organic electro-luminescence devices according to the related art, the design of TFTs is easy and the aperture ratio is high. Thus, it is advantageous in view of the lifetime of the products. However, because the cathode is disposed on the organic electro-luminescent layer, material selection is restricted. As a result, the transmittance is limited and the luminous efficiency is degraded.